The manufacture of metallic fibers including aluminum fibers is already carried out. For example, JP 59-82411 A discloses a method and apparatus for manufacturing fibers of a metal or alloy thereof by keeping the metal or alloy thereof in a molten state in a closed vessel, supplying a pressurized gas into a crucible in the closed vessel to press the molten metal in order to raise a molten metal feed pipe, and ejecting the molten metal from ejection holes of a nozzle into the atmosphere to be quenched and solidified.
Since molten aluminum is ejected and discharged from pores with 0.08 mm Ø into the atmosphere to manufacture aluminum fibers by the method of the above publication, non-metallic inclusions in the molten aluminum are caught in the pores to make a jet from the pores imperfect or cause partial occlusion of some of the plural pores.
When preheating of a fireproof nozzle body constituting the plural pores is incomplete, the molten aluminum extruded from the inside of the above crucible is solidified instantaneously in the plural pores to occlude most of the plural pores, thereby interrupting an operation.
JP 62-294104 A discloses a method of manufacturing a porous metal body by dropping metallic fibers to deposit on one end of a belt conveyor and press molding them at the other end of the belt conveyor.
When molten aluminum is ejected from the ejection holes of the nozzle into the atmosphere, aluminum fibers manufactured by quenching and solidifying float in the air. Therefore, even when they drop on the above belt conveyor, they hardly drop at a uniform density and the areal (surface) density (g/m2) of the porous metal body of the aluminum fibers press-molded at the other end of the belt conveyor tends to become extremely nonuniform. Accordingly, when it is used as a sound absorbent material or electromagnetic shielding material, its characteristics become unstable and a quality problem easily occurs.
When an aluminum fiber porous body (to be referred to as aluminum fiber nonwoven fabric hereinafter) is to be manufactured using the prior art as described above, if non-metallic inclusions in molten aluminum are caught in the pores (to be referred to as ejection holes hereinafter) of a nozzle body made of a refractory (to be referred to as ejection nozzle hereinafter) and adhered to the ejection holes, an imperfect ejection state is created and a jet of the molten aluminum is greatly disturbed, thereby causing the deterioration of a quality of an aluminum fiber nonwoven fabric. When the preheating of the ejection nozzle is insufficient, molten aluminum which reaches the inside of the ejection nozzle is instantaneously solidified at the beginning of ejection, whereby most of the ejection holes are occluded and the operation is suspended.
Further, when aluminum fibers ejected from the ejection nozzles fly nonuniformly in the air, the amount of the fibers dropped on the belt conveyor becomes nonuniform, with the result that the areal density of the nonwoven fabric becomes nonuniform and there are variations in the quality and characteristics such as sound absorption coefficients of the nonwoven fabric.
It is an object of the present invention to provide an apparatus for manufacturing a metallic fiber nonwoven fabric having stable quality and characteristics which solve the above problems of the prior art, a method of manufacturing an aluminum fiber nonwoven fabric having stable quality and characteristics using the apparatus, and a method of manufacturing a laminated aluminum material.
The inventors of the present invention have come across the above problems in the research and development process of an aluminum fiber nonwoven fabric, have conducted intensive experimental studies and have found that the object of the present invention can be attained by the apparatus and methods of the present invention. The present invention has thus been accomplished based on the finding. Note that reference numerals in the following description are given for the reference of the accompanying drawings. The present invention is not limited to examples shown in these drawings.